The fourth Generation (4G) of mobile communications standardized Long Term Evolution (LTE) and LTE-Advanced (LTE-A) technologies in order to provide higher data rates to consumers. 4G is being deployed on new and different frequency bands around the globe, however, which has led to band proliferation. Consequently, where it is desired for users to be able to maintain connectivity over any of these 4G frequency bands, device antennas need to cover about 40 bands in Frequency Division Duplex (FDD) and Time Division Duplex (TDD), with the number of bands likely to increase further in future generations. In this regard, world-wide mobile data access has multiplied the number of bands allocated to mobile communication by a factor of ten compared to speech-only specifications (e.g., 2G). Specifically, fourteen bands are defined in the low frequency range of the 4G spectrum today and represent nearly all the frequencies between 699 MHz and 960 MHz. Additionally, part of the frequency spectrum previously used for television broadcasting in frequencies ranging from 600 MHz to 698 MHz is being put up for auction to carriers, and still lower frequencies are being considered.
Designing a handset antenna in the low bands of 4G has shown to be a challenge for antenna engineers, as the antenna bandwidth and operating frequency vary inversely proportionally with the antenna volume provided a constant efficiency. Thus, to both lower the antenna resonance frequency and to enhance its bandwidth, the antenna volume needs to be increased. Conversely, however, consumer demand for smaller and slimmer designs, along with the drive to fit more components into smart-phones (e.g., cameras, large battery, high-end screen), incentivizes device manufacturers to develop antenna footprints that are as small as possible for newer generations of smart-phones. As a result, over the past decade, antenna engineers have pushed the low bound of their design from 824 MHz to 699 MHz while at the same time reducing the antenna volume. This combination of low resonance frequency and smaller antenna volume can often cause efficiency degradation, which impacts communication performance. These problems may be further exacerbated by attempts to utilize the new bands available in the low band, which have to be pushed by an extra 100 MHz.
Accordingly, it would be desired for antenna systems, devices, and methods to provide efficient coverage of low frequency bands (e.g., 700 MHz-bands and 600 MHz-bands) for the new generations of mobile communication.